In fluid control systems, for example a hydraulic system of an excavator, there are often a plurality of pumps serving a plurality of hydraulic circuits each of which supply fluid to one or more work elements. The pressure and fluid rate requirements of the different work elements often vary markedly between the elements.
In order to prevent waste of labor and materials, it is therefore desirable to solve the problem of providing a control system which will function to control the pump of a fluid circuit in response to the operational mode of the work elements served by the particular circuit. By so constructing the control system, work elements of widely varying maximum pressure construction can be served by a single fluid circuit.
The present invention is directed to overcoming the problems as set forth above.
In accordance with this invention, a fluid system has first and second circuits each having a variable displacement pump serving first and second work elements through respective first and second directional control valves. The first and second pumps are associated with a summing valve for controlling the rate of discharge of the pumps. A first means is provided for controlling the output of one of the pumps of a selected circuit in response to a signal delivered from the summing valve during operation of the work elements of both of the circuits and for controlling the output of said one of the pumps by a modified pilot pressure signal in response to the operation of only the work element of the selected one of the circuits having said one of the pumps.